The present invention relates to a method and an apparatus for performing welding with respect to a workpiece.
FIG. 9 illustrates an example of prior art welding apparatus. The illustrated welding apparatus comprises a combination of a positioner 8 and a welding robot 9. The positioner 8 is of a so-called trunnion type and includes a rotary table 80 supported on a base frame 81. The rotary table 80 is rotatable about both of two axes C1, C2. The axis C2 extends perpendicularly to the sheet surface. The rotary table 80 has an upper surface for mounting a workpiece W. The welding robot 9 comprises a robot body 90, and a controller 91 including a teaching box for controlling the robot body 90. The robot body 90 has an articulated structure which includes a plurality of arms 90a-90c connected together for rotation relative to each other. The arm 90c has a tip end which carries a welding torch 3. The robot body 90 is mounted independently of the positioner 8.
With the welding apparatus having the above-described structure, it is possible to set the workpiece W at a position or in a posture suitable for welding by operating the rotary table 80 of the positioner 8. For example, a fillet portion Wb of the workpiece W can be oriented upwardly by inclining the rotary table 80 as illustrated in the figure. In this state, welding for the fillet portion Wb can be performed with the torch 3 oriented vertically or generally vertically downward for facing the fillet portion Wb. If the torch 3 is oriented horizontal or upward in arc welding, a failure may occur in welding. However, the welding apparatus having the above-described structure can eliminate the possibility of such a failure. Further, by performing welding with the fillet portion Wb oriented upward, it is possible to prevent a weld bead from localizing at one side of the fillet portion Wb.
However, the above-described prior art welding apparatus has the following drawbacks.
In the above-described structure, the robot body 90 is mounted independently of the positioner 8. Therefore, when an error of the rotational angle occurs in rotating the rotary table 80 about the shaft C2 through a predetermined angle, the position of the workpiece W relative to the robot body 90 deviates from the intended position. In rotating the rotary table 80, the moving amount of a specific portion of the workpiece W is the product of the distance from the rotational center of the rotary table 80 to that specific portion and the rotational angle (radian) of the rotary table 80. Therefore, even when the rotational angle error is small, the error of the moving amount may be large at a portion located relatively far from the rotational center of the rotary table 80. As a result, the positional deviation of the workpiece W relative to the robot body 90 may be significant. When the welding robot 9 is operated in this state, a failure occurs in welding.
In this way, in the above-described prior art apparatus, a welding failure due to an error of the movement of the positioner 8 occurs when the positioner 8 and the welding robot 9 are controlled independently of each other. To eliminate the possibility of such a failure, it is necessary to utilize numerical control not only for the welding robot 9 but also for the positioner 8 so that the welding robot 9 and the positioner 8 are controlled in highly precise relationship. However, such an arrangement is costly because it requires an expensive positioner 8 as well as a control program for the positioner 8. Further, the positioner 8 and the welding robot 9 must undergo a complicated teaching process to result in difficulty of handling the apparatus.
Other examples of prior art welding apparatuses are disclosed in JP-A-4-262873 and JP-A-9-277050. Either of these welding apparatuses comprises a first table movable in one direction and a second table mounted on the first table for supporting a workpiece. The second table is movable in a direction which is different from the moving direction of the first table. A robot body of a welding robot is mounted on the first table. With this structure, a change in the posture or orientation of the workpiece caused by a movement of the second table also results in a change in the relative positional relationship between the workpiece supported on the second table and the robot mounted on the first table. Therefore, the welding apparatuses disclosed in the above-identified publications have the same drawbacks as those of the prior art apparatus shown in FIG. 9.
An object of the present invention is to provide a welding method and a welding apparatus capable of eliminating or lessening the problems of the above-described prior art.
According to a first aspect of the present invention, there is provided a welding method for performing welding with respect to a workpiece by using a positioner provided with workpiece supporting means which is rotatable about a first central axis and is pivotable up and down about a second central axis crossing the first central axis, and a welding robot including a robot body for moving a torch, wherein the welding is performed with both the workpiece and the robot body carried by the workpiece supporting means.
According to a second aspect of the present invention, there is provided a welding apparatus comprising a positioner provided with workpiece supporting means which is rotatable about a first central axis and is pivotable up and down about a second central axis crossing the first central axis, and a welding robot including a robot body for moving a torch, wherein the robot body is carried by the workpiece supporting means.
According to the present invention, the robot body of the welding robot is carried by the workpiece supporting means of the positioner. Therefore, it is possible to prevent the positional relationship between the workpiece supporting means and the robot body from changing when the workpiece supporting means is operated. Accordingly, it is also possible to prevent the robot body from changing its position relative to the workpiece supported on the workpiece supporting means. Specifically, even when the workpiece supporting means is rotated about the first central axis or pivoted up and down about the second central axis, it is possible to keep unchanged the relative positional relationship between the robot body and the workpiece. As a result, according to the present invention, even when any error occurs in the operation of the work supporting means, it is possible to locate the torch at a position close to and in facing relationship to an intended portion of the workpiece without being influenced by the error.
Therefore, unlike the prior art apparatus, it is possible, in the present invention, to eliminate or lessen the need for controlling the positioner in highly precise relationship to the robot body. Thus, use may be made of an inexpensive positioner. Further, it is possible to dispense with a program for numerical control of the positioner or to make the content of such a program simpler. Moreover, the welding apparatus needs only to undergo a simpler teaching process.
Of course, by the operation of the positioner, it possible to set the posture or orientation of the workpiece suitably for the welding operation by the welding robot, so that welding can be performed appropriately according to the present invention.
Preferably, the robot body my comprise a base, and a plurality of arms a base end supported by the base and connected to each other for relative rotation. The plurality of arms also have a three-dimensionally movable tip end which is provided with holding means for holding the torch.
With this structure, the robot body is capable of three-dimensionally moving the torch, which is suitable for performing various types of welding operation.
Preferably, the welding apparatus may further comprise robot moving means supporting the base of the robot body for moving the robot body on or above the workpiece supporting means.
With this structure, it is possible to move the entire robot body to a position suitable for welding depending on the configuration or size of the workpiece. Therefore, this structure is suitable for performing welding for plural kinds of workpieces which differ from each other in configuration or size.
Preferably, the robot moving means may comprise a frame including at least one post standing from the workpiece supporting means and a beam extending from an upper portion of the post in a direction crossing the first central axis. The robot moving means may also comprise a support member for supporting the base of the robot body. The support member may be movable longitudinally of the beam while being guided by the beam.
With this structure, it is possible to move the robot body above the workpiece supporting means in a direction crossing the first central axis. Therefore, it is possible to locate the robot body relative to the workpiece at a position suitable for the welding operation.
Preferably, the frame may be movable in a direction crossing the longitudinal direction of the beam.
With this structure, it is possible to move the robot body longitudinally of the beam as well as in the direction crossing the longitudinal direction of the beam. Therefore, this structure is more preferable for locating the robot body at a position suitable for the welding.
Preferably, the base of the robot body may be fixedly mounted on the workpiece supporting means.
Preferably, the robot body may be mounted on the workpiece supported on the workpiece supporting means for causing the workpiece supporting means to carry the robot body.
According to a third aspect of the present invention, there is provided a welding method for performing welding with respect to a workpiece by using a positioner for changing posture or orientation of the workpiece and a welding robot including a robot body for moving a torch, wherein the welding is performed with the robot body being mounted on the workpiece.
Also with this welding method, it is possible to keep the relative positional relationship between the workpiece and the robot body unchanged during the operation of the positioner. Therefore, it is possible to obtain the same advantages as those obtained by the welding method and the welding apparatus according to the first and the second aspects of the present invention.